U.S. patent application number 11/077500 was filed with the patent office on 2005-09-29 for positioning and locking mechanisms and articles that employ the same.
Invention is credited to Browne, Alan L., Meernik, Paul R..
Application Number | 20050210874 11/077500 |
Document ID | / |
Family ID | 34988125 |
Filed Date | 2005-09-29 |
United States Patent
Application |
20050210874 |
Kind Code |
A1 |
Browne, Alan L. ; et
al. |
September 29, 2005 |
Positioning and locking mechanisms and articles that employ the
same
Abstract
Disclosed herein is a locking mechanism for positioning or
locking an article comprising a housing 3; an optional active
element 6 in operative communication with a connecting means 22,
wherein the active element 6 and the connecting means 22 are
disposed within the housing 3; wherein the active element 6 upon
being activated is capable of exerting a force on the connecting
means 22; a compression initiation element 4 located within the
housing 3, wherein the compression initiation element 4 comprises a
shape memory material, and wherein the compression initiation
element 4 upon activation facilitates the activation of the active
element 6; and a spring stack 8 disposed adjacent to the
compression initiation element 4, wherein the spring stack 8 is in
operative communication with the compression initiation element 4
and wherein the spring stack 8 is configured to radially expand
within the housing 3.
Inventors: |
Browne, Alan L.; (Grosse
Pointe, MI) ; Meernik, Paul R.; (Redford,
MI) |
Correspondence
Address: |
KATHRYN A MARRA
General Motors Corporation, Legal Staff
Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
34988125 |
Appl. No.: |
11/077500 |
Filed: |
March 9, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60552878 |
Mar 12, 2004 |
|
|
|
Current U.S.
Class: |
60/527 |
Current CPC
Class: |
F03G 7/065 20130101 |
Class at
Publication: |
060/527 |
International
Class: |
C06C 005/06; F01B
029/10; F02G 001/04 |
Claims
What is claimed is:
1. A locking mechanism for positioning or locking an article
comprising: a housing; an optional active element in operative
communication with a connecting means, wherein the active element
and the connecting means are disposed within the housing; wherein
the active element upon being activated is capable of exerting a
force on the connecting means; a compression initiation element
located within the housing, wherein the compression initiation
element comprises a shape memory material, and wherein the
compression initiation element upon activation facilitates the
activation of the active element; and a spring stack disposed
adjacent to the compression initiation element, wherein the spring
stack is in operative communication with the compression initiation
element and wherein the spring stack is configured to radially
expand within the housing.
2. The locking mechanism of claim 1, wherein the shape memory
material comprises a composition that has the ability to remember
its original shape upon the application of an activation
signal.
3. The locking mechanism of claim 2, wherein the activation signal
is a change in temperature.
4. The locking mechanism of claim 1, wherein the spring stack
undergoes radial expansion upon being compressed, and wherein the
radial expansion of the spring stack promotes locking of an article
that is in operative communication with the locking mechanism.
5. The locking mechanism of claim 1, wherein the housing houses the
active element, the connecting means, the compression initiation
element, and the spring stack and wherein the connecting means is
in slideable communication with the housing.
6. The locking mechanism of claim 5, wherein the active element,
the connecting means, and the spring stack act cooperatively with
each other to permit positioning and/or locking of an article that
is in communication with the locking mechanism.
7. The locking mechanism of claim 1, wherein the compression
initiation element in its original state is in circumferential
contact with an inner surface of a housing that houses the
compression initiation element, and wherein the compression
initiation element in its original shape applies a radial load
against the inner surface of the housing.
8. The locking mechanism of claim 1, wherein the compression
initiation element comprises a split ring that comprises a
circumferential slot into which is disposed a ring, wherein the
ring comprises a shape memory material.
9. The locking mechanism of claim 1, wherein the compression
initiation element comprises a circular hoop element, with a
cross-member manufactured from a smart material that can contract
upon activation and wherein the circular hoop element upon
deformation contacts the inner surface of the housing.
10. The locking mechanism of claim 1, wherein the connecting means
comprises a shaft upon which are disposed two cylindrical discs, a
first disc and a second disc, wherein connecting means is in
slideable communication with a housing and wherein a compression
initiation element and a spring stack are disposed between the
first cylindrical disc and the second cylindrical disc.
11. The locking mechanism of claim 10, further comprising a second
compression initiation element disposed between the first
cylindrical disc and the second cylindrical disc.
12. The locking mechanism of claim 1, wherein the active element
comprises an expansion spring and/or a retraction spring and
wherein the expansion spring and/or the retraction spring comprises
a shape memory material.
13. The locking mechanism of claim 1, wherein the locking mechanism
is capable of resisting a compressive force and/or a tensile
force.
14. The locking mechanism of claim 1, wherein the locking mechanism
is capable of infinite detent.
15. A method for operating a locking mechanism comprising:
activating a compression initiation element that comprises a shape
memory material by the application of an external stimulus;
decompressing a spring stack, wherein the spring stack comprises
one or more springs; activating an optional active element in a
manner effective to displace a connecting means disposed between an
article and a reference frame, wherein the compression initiation
element, the spring stack and the connecting means are all disposed
within a housing.
16. The method of claim 15, wherein the activating of the
compression initiation element reduces the radial load and the
axial friction between the compression initiation element and the
housing as well as between the spring stack and the housing.
17. The method of claim 15, wherein activating the compression
initiation element comprises heating the shape memory material
above its transition temperature and enabling it to apply a
compressive force on the compression initiation element.
18. The method of claim 15, wherein decompressing the spring stack
promotes radial contraction of the springs in the stack, and
wherein the radial contraction promotes a reduction in the axial
friction between the spring stack and the housing.
19. The method of claim 15, further comprising radially expanding
the springs in the spring stack to promote locking of the article
with respect to the reference frame.
20. The method of claim 15, wherein activating the active element
comprises expanding an expansion spring and/or retracting a
retraction spring.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/552,878 filed Mar. 12, 2004, the entire
contents of which are hereby incorporated by reference.
BACKGROUND
[0002] This disclosure relates to a positioning and locking
mechanism and articles that utilize these mechanisms.
[0003] Numerous devices use linear actuators for purposes of
positioning articles such as entrances (doors) in automobiles and
residential buildings, jaws of power tools, platens in
manufacturing devices such as injection molding machines,
compression molding machines, band saws, or the like. Actuators
commonly use a combination of pneumatic and electrical devices to
achieve such positioning. However, the use of pneumatic and
electrical actuators are expensive and occupy an extensive amount
of space. It is therefore desirable to use actuators for
positioning that are compact, consume less power, are easily
controllable and can provide accuracy and sensitivity to the
device.
SUMMARY
[0004] Disclosed herein is a locking mechanism for positioning or
locking an article comprising a housing; an active element in
operative communication with a connecting means, wherein the active
element and the connecting means are located in the housing;
wherein the active element upon being activated is capable of
exerting a force on the connecting means; a compression initiation
element located within the housing, wherein the compression
initiation element comprises a shape memory material, and wherein
the compression initiation element upon activation facilitates the
activation of the active element; and a spring stack disposed
adjacent to the compression initiation element, wherein the spring
stack is in operative communication with the compression initiation
element and wherein the spring stack is configured to radially
expand within the housing.
[0005] Disclosed herein too is a locking mechanism for positioning
or locking an article comprising a housing; an active element in
operative communication with a connecting means, wherein the active
element upon being activated is capable of exerting a force on the
connecting means, and wherein the connecting means is in slideable
communication with the housing and wherein the connecting means is
in operative communication with a reference frame and the article;
a spring stack and a compression initiation element that act as a
restraint upon the active element, wherein the compression
initiation element upon activation facilitates the activation of
the active element, and wherein the spring stack is in operative
communication with the connecting means and with the compression
initiation element; wherein the housing houses the active element,
the compression initiation element and the spring stack.
[0006] Disclosed herein too is a method for operating a locking
mechanism comprising activating a compression initiation element
that comprises a shape memory material by the application of an
external stimulus; decompressing a spring stack, wherein the spring
stack comprises one or more springs; activating an active element
in a manner effective to displace a connecting means disposed
between an article and a reference frame, wherein the compression
initiation element, the spring stack and the connecting means are
all disposed within a housing.
DESCRIPTION OF FIGURES
[0007] Referring now to the figures, which are exemplary
embodiments, and wherein like elements are numbered alike:
[0008] FIG. 1 is a depiction of one exemplary embodiment of a
locking mechanism 2, wherein a smart material, preferably a shape
memory alloy is used to activate the positioning of an article
60;
[0009] FIG. 2 depicts one exemplary embodiment of a compression
initiation element 4;
[0010] FIG. 3 depicts another exemplary embodiment of a compression
initiation element 4;
[0011] FIG. 4 is a depiction of the terms upstream and downstream
as they apply to the disclosed locking mechanisms;
[0012] FIG. 5 is a depiction of one exemplary embodiment of a
locking mechanism 2 that can be used to resist compressive forces
on the locking mechanism 2;
[0013] FIG. 6 is a depiction of one exemplary embodiment of a
locking mechanism 2 that can be used to resist tensile forces on
the locking mechanism 2; and
[0014] FIG. 7 is a depiction of one exemplary embodiment of a
locking mechanism 2 that can be used to resist both tensile forces
and compressive forces on the locking mechanism
DETAILED DESCRIPTION
[0015] Disclosed herein is a wave spring locking mechanism that
enables the positioning and/or locking or an article with respect
to a reference frame. The article may be any device that utilizes
spatial positioning such as a door in an automobile or a
residential building; the hood or trunk of a automobile; the jaws
of a vice or a press; the platens on machine tools such as
injection molding machines, compression molding machines; arbors
and chucks on lathes and drilling machines, or the like. The
reference frame can comprise a door frame, an automobile frame, a
aircraft frame, a ship frame, or the like, to which the movable
article is in communication with. While the position of the
reference frame is generally fixed, in certain situations, both the
article and the reference frame are mobile and can be
displaced.
[0016] In one embodiment, the positioning or repositioning of an
article that is in operative communication with the locking
mechanism is accomplished by the application of a suitable manual
force. In another embodiment, the positioning or repositioning of
an article that is in operative communication with the locking
mechanism is accomplished by use of a motive force such as
mechanical energy or electrical energy. Positioning or
repositioning is defined as the motion imparted to the article by
manual force or other motive forces such as mechanical energy,
electrical energy, or the like. The ability to position and lock an
article in a state of equilibrium at any desirable point along the
length of its travel is termed detent. The locking mechanisms
described below have an infinite detent capability and permit
positioning or repositioning of the article at any degree of
opening with the minimal use of force.
[0017] In one embodiment, the locking mechanism is a wave spring
mechanism. The wave spring locking mechanism is advantageous in
that it permits positioning at any height or degree of opening
depending upon the physical characteristics of the person opening
the article. The detent capability exhibited by the wave spring
locking mechanism may be advantageously employed in automobile lift
gates, tail gates, doors, hoods, trunks, or the like. They may also
be advantageously employed in windows and doors for aircraft,
ships, residential and office buildings. The wave spring locking
mechanism may be advantageously employed in storm doors for
residential and office buildings.
[0018] Referring now to an exemplary embodiment depicted in the
FIG. 1, the locking mechanism 2 comprises a housing 3 in which is
disposed a compression initiation element 4, an optional active
element 6, a spring stack 8 and a communication means 22. The
active element 6 is optional and its exclusion from the locking
mechanism 2 would permit the user to manually control the
displacement of the locking mechanism 2. The locking mechanism 2 is
disposed between a reference frame 50 and the article 60 whose
position is to be controlled. The connecting means 22 is in
operative communication with the reference frame 50 and/or the
article 60. In one embodiment, the compression initiation element
4, the active element 6 and the spring stack 8 act cooperatively to
facilitate the positioning and locking of the article 60.
[0019] The housing 3 is of a length effective to permit the article
60 to accomplish its entire range of desired motion. The housing 3
may be manufactured from a metal, a ceramic, a polymer, or a
combination comprising at least one of the foregoing. The housing 3
may also be manufactured from a composite such as, for example, a
graphitic composite. The inner wall of the housing 3 may be
optionally coated with a coating such as polytetrafluoroethylene
that reduces friction. The housing 3 may have any desired
cross-sectional shape such as circular, square, triangular or the
like. In an exemplary embodiment, the housing 3 has a circular
cross-section.
[0020] The connecting means 22 is in slideable communication with
the housing 3 and comprises a shaft 23 upon which are affixed two
cylindrical discs, a first disc 24 and a second disc 25. The first
cylindrical disc 24 and the second cylindrical disc 25 are disposed
upon on the shaft 23 at a distance apart from each other. Disposed
between the first cylindrical disc 24 and the second cylindrical
disc 25 are the compression initiation element 4 and the spring
stack 8. The active element 6 is generally disposed on the side of
the connecting means 22 that is closer to the reference frame 50.
The active element 6 is in operative communication with the
connecting means 22 and imparts displacement to the connecting
means 22 upon activation of the compression initiation element 4.
In one embodiment, the longitudinal axis of the compression
initiation element 4, the active element 6, the spring stack 8
and/or the connecting means 22 are coincident with the longitudinal
axis of the housing 3. The longitudinal axis of the housing 3 is
depicted by the line AA' and is parallel to the y-axis indicated in
the FIG. 1. In one embodiment, the connecting means 22 is in
slideable communication with the housing 3 and reciprocates in a
manner such that its longitudinal axis is coincident with the line
AA'. In another embodiment, the connecting means 22 reciprocates in
a manner such that its longitudinal axis is parallel with the line
AA'. For purposes of this disclosure, displacement or movement
along the line AA' is termed axial movement and frictional forces
that act in a direction that is parallel to the line AA' is termed
axial friction.
[0021] The compression initiation element 4 comprises a smart
material of the class that can undergo a change in shape and/or
stiffness upon activation. Activation refers to the application of
an external stimulus when the element that is activated comprises a
smart material. The compression initiation element, by itself, is
not designed to restrain a spring or lock the linear actuator
against applied loads. Its purpose is to provide a small axial load
against which some of the springs in the spring stack can be
loaded, thereby generating a greater axial restraining load against
which more springs may be compressed if needed.
[0022] Therefore, the compression initiation element 4 in the
un-activated state facilitates the compression of the spring stack
8, which facilitates the locking of the article 60. Upon being
activated, the compression initiation element 4 facilitates a
reduction of compressive forces on the spring stack 8, thereby
permitting activation of the active element 6, which facilitates
the displacement of the connecting means 22 and hence the movement
of the article 60. Details of the compression initiation elements 4
are shown in the FIGS. 2 and 3 and are explained below.
[0023] FIG. 2 is one exemplary depiction of the side view and front
view of one embodiment of the compression initiation element 4. In
this embodiment, the compression initiation element 4 comprises a
split ring 10 that comprises a circumferential slot 12 into which
is disposed a ring 14. Both the split ring 10 and the ring 14 can
be manufactured from smart materials. In one embodiment, the smart
materials used in the locking mechanism 2 are shape memory
materials. Shape memory materials generally refer to materials or
compositions that have the ability to remember their original
shape, which can subsequently be recalled by applying an external
stimulus, i.e., an activation signal. As such, deformation of the
shape memory material from the original shape can be a temporary
condition, which can be used for fixturing a variety of workpieces
having different surface contours. Exemplary shape memory materials
suitable for use in the present disclosure include shape memory
alloys and ferromagnetic shape memory alloys and composites of the
foregoing shape memory materials with non-shape memory materials,
and combinations comprising at least one of the foregoing shape
memory materials. In another embodiment, the class of smart
materials used in the locking mechanism 2 are those that change
their shape in proportion to the strength of the applied field but
then return to their original shape upon the discontinuation of the
field. Exemplary smart materials in this category are shape memory
alloys, electroactive polymers (dielectric polymers),
piezoelectrics, and piezoceramics.
[0024] For convenience and by way of example, reference herein will
be made to shape memory alloys. An exemplary smart material for the
ring 14 is a shape memory alloy.
[0025] The unconstrained outer diameter of the split ring 10 is
selected to be slightly greater than the inner diameter of the
housing 3. The split ring 10 is compressed and inserted into the
housing 3, in a manner similar to a piston ring that is compressed
and inserted into a cylindrical bore. When the diameter of the
split ring 10 is unconstrained, the split ring 10 exerts a radial
force against the inner surface of the housing 3, such that the
resulting axial friction is sufficient to cause the spring stack 8
to lock and thereby restraining the active element 6. As noted
above the split ring 10 can be manufactured from a smart
material.
[0026] As detailed above, the ring 14 is disposed in the
circumferential slot 12 of the compression initiation element 4.
The ring 14 can comprise one or more turns of SMA wire. The force
desirable to compress the split ring 10 and to reduce the axial
friction between the split ring 10 against the inner surface of the
housing 3 could be used to determine the number of turns of the SMA
wire used to form the ring 14. Alternatively, the ring 14 can
comprise a solid band manufactured from an SMA. The solid can have
a circular cross-section, a rectangular cross-section, or the
like.
[0027] Shape memory alloys (SMA's) generally refer to a group of
metallic materials that demonstrate the ability to return to some
previously defined shape or size when subjected to an appropriate
thermal stimulus. Shape memory alloys are capable of undergoing
phase transitions in which their flexural modulus (stiffness),
yield strength, and shape orientation are altered as a function of
temperature. Generally, in the low temperature, or martensite
phase, shape memory alloys can be plastically deformed and upon
exposure to some higher temperature will transform to an austenite
phase, or parent phase, returning to their shape prior to the
deformation. Materials that exhibit this shape memory effect only
upon heating are referred to as having one-way shape memory. Those
materials that also exhibit shape memory upon re-cooling are
referred to as having two-way shape memory behavior.
[0028] Shape memory alloys can exhibit a one-way shape memory
effect, an intrinsic two-way effect, or an extrinsic two-way shape
memory effect depending on the alloy composition and processing
history. Annealed shape memory alloys typically only exhibit the
one-way shape memory effect. Sufficient heating subsequent to
low-temperature deformation of the shape memory material will
induce the martensite to austenite type transition, and the
material will recover the original, annealed shape. Hence, one-way
shape memory effects are only observed upon heating.
[0029] Intrinsic and extrinsic two-way shape memory alloys are
characterized by a shape transition both upon heating from the
martensite phase to the austenite phase, as well as an additional
shape transition upon cooling from the austenite phase back to the
martensite phase. Active elements that exhibit an intrinsic one-way
shape memory effect are fabricated from a shape memory alloy
composition that will cause the active elements to automatically
reform themselves as a result of the above noted phase
transformations. Intrinsic two-way shape memory behavior must be
induced in the shape memory material through processing. Such
procedures include extreme deformation of the material while in the
martensite phase, heating-cooling under constraint or load, or
surface modification such as laser annealing, polishing, or
shot-peening. Once the material has been trained to exhibit the
two-way shape memory effect, the shape change between the low and
high temperature states is generally reversible and persists
through a high number of thermal cycles. In contrast, active
connector elements that exhibit the extrinsic two-way shape memory
effects are composite or multi-component materials that combine a
shape memory alloy composition that exhibits a one-way effect with
another element that provides a restoring force to return the first
plate another position or to its original position.
[0030] The temperature at which the shape memory alloy remembers
its high temperature form when heated can be adjusted by slight
changes in the composition of the alloy and through heat treatment.
In nickel-titanium shape memory alloys, for instance, it can be
changed from above about 100.degree. C. to below about -100.degree.
C. The shape recovery process occurs over a range of just a few
degrees and the start or finish of the transformation can be
controlled to within a degree or two depending on the alloy
composition.
[0031] Suitable shape memory alloy materials for fabricating the
active elements include nickel-titanium based alloys,
indium-titanium based alloys, nickel-aluminum based alloys,
nickel-gallium based alloys, copper based alloys (e.g., copper-zinc
alloys, copper-aluminum alloys, copper-gold, and copper-tin
alloys), gold-cadmium based alloys, silver-cadmium based alloys,
indium-cadmium based alloys, manganese-copper based alloys,
iron-platinum based alloys, iron-palladium based alloys, or the
like, or a combination comprising at least one of the foregoing
shape memory alloys. The alloys can be binary, ternary, or any
higher order so long as the alloy composition exhibits a shape
memory effect, e.g., change in shape orientation, changes in yield
strength, and/or flexural modulus properties, damping capacity, and
the like.
[0032] The thermal activation signal may be applied to the shape
memory alloy in various ways. It is generally desirable for the
thermal activation signal to promote a change in the temperature of
the shape memory alloy to a temperature greater than or equal to
its austenitic transition temperature. Suitable examples of such
thermal activation signals that can promote a change in temperature
are the use of steam, hot oil, resistive electrical heating, or the
like, or a combination comprising at least one of the foregoing
signals. A preferred thermal activation signal is one derived from
resistive electrical heating.
[0033] Referring once again to the FIG. 2, when the ring 14 is
activated by raising its temperature above its transition
temperature, the ring changes its original shape and takes on a
preset shape that has a smaller diameter than the original shape.
The change to a smaller diameter results in the compression of the
split ring 10. The compression of the split ring 10 results in the
removal of the radial load imposed by the split ring 10 on the
housing 3.
[0034] If the ring 14 is manufactured from a two way shape memory
alloy, the split ring 10 can be returned to its original shape upon
cooling the ring 14 to its original temperature. Alternatively, the
split ring 10 can be returned to its original shape by heating the
ring 14 to a second transformation temperature.
[0035] Another embodiment of a compression initiation element 4 is
shown in the FIG. 3. While the split ring compression initiation
element 4 depicted in FIG. 2 provides friction in its original
state during which the ring 14 is not activated, the compression
initiation element 4 can also be designed to provide axial friction
only after a stimulus is applied to activate the compression
initiation element 4. This is depicted in the FIG. 3. In this
embodiment, the compression initiation element 4 comprises a
circular hoop element 11, with a cross-member 13 manufactured from
a smart material that can contract upon activation. The circular
hoop element 11 floats freely in the housing 3. The cross-member
can be a wire. When the cross-member is activated (e.g., by the
application of heat) it contracts and deforms the circular hoop
element 11. The circular hoop element 11 upon deformation contacts
the inner surface of the housing 3, increasing the axial
friction.
[0036] The circular hoop element 11 can also be made from smart
materials if desired. Suitable smart materials are shape memory
alloys.
[0037] With reference again to the FIG. 1, the optional active
element 6 comprises an expansion spring that is normally under
compression. When the optional active element 6 is excluded from
the locking mechanism 2, manual control can be exerted over the
displacement of the article 60 along its entire range of travel
after activation of the compression initiation element 4.
Additional springs can be used in the active element 6 if desired.
As will be shown in subsequent embodiments, some of these springs
can be retracting springs. The expanding and retracting springs are
generally coil springs. The expansion spring facilitates the
positioning of the article 60 when the constraining forces upon it
are removed. The expansion spring has a spring constant effective
to displace the article 60 once the constraining force on the split
ring 10 is removed. The expansion spring generally expands and
contracts along the axis AA'.
[0038] The spring stack 8 comprises one or more springs that are
capable of expanding radially upon being compressed and provides
axial friction between the outer circumferential edge of the
individual springs and the inner surface of the housing 3. The
axial friction between the outer circumferential edge of the
individual wave springs and the inner wall of the housing 3
provides the restraining force necessary to hold active element 6
in its compressed or expanded state until an activation signal
causes the split ring to contract.
[0039] In one embodiment, the spring stack 8 comprises wave
springs. The wave spring stack comprises one or more wave springs
and facilitates the locking of the article 60 when the compression
initiation element 4 contacts the inner surface of the housing 3.
When the wave spring stack comprises more than one wave springs, a
washer may be disposed between the wave springs thereby separating
some of the wave springs from the others. As can be seen in the
FIG. 1, in one embodiment, it is generally desirable to dispose one
wave spring between the compression initiation element 4 and the
washer, with multiple wave springs disposed between the connecting
means 22 and the washer.
[0040] When a compressive force is applied to the wave spring
stack, the individual wave springs expand radially outwards and
exert a radial load or force against the inner walls of the housing
3, thus facilitating the locking of the article 60. In one
embodiment, in order to facilitate the unlocking of the wave spring
stack 8, the wave spring stack is designed such that radial contact
between the wave springs and the inner wall of the housing 3 occurs
only on the upstream portion of the wave spring relative to the
compressive initiation element 4. This upstream position of the
wave spring stack is shown in the FIG. 4 and refers to that
position on the stack that is closer to the reference frame 50 than
the article 60. The unlocking of the wave-spring stack can be
accomplished by activating the compression initiation element 4 and
thereby removing the axial restraining load on the spring stack 8.
The downstream portions of the wave spring are then be free to move
axially, thus relaxing the radial and the frictional loads between
the wave springs and the inner wall of the housing 3.
[0041] In one embodiment, in one manner of operating the locking
mechanism 2, when it is desired to change the position of the
article 60 from a first position to a second position, the
temperature of the ring 14 is increased using electrical resistive
heating, i.e., the ring 14 is activated. Upon heating the ring 14
above its transition temperature, the SMA wire applies a
compressive force on the split ring 10, which causes it to contract
radially. The radial contraction of the split ring 10 removes the
radial load exerted on the housing 3 and reduces the axial friction
between the housing 3 and the compression initiation element 4 as
well as the axial friction between the housing 3 and the spring
stack 8. The radial contraction of the split ring 10 facilitates
the decompression of the springs in the spring stack 8, thereby
reducing axial friction between the housing 3 and the spring stack
8. The reduction in the axial friction permits the activation of
the expansion spring, thereby facilitating the movement of the
article 60 from its first position to its second position. The
direction of movement of the article 60 during its displacement
from its first position to the second position is shown in the FIG.
1. The term "activation" as used herein refers to the selective
application of an external stimulus to the smart material (shape
memory material). It also applies to the removal of a constraint on
the active element 6 thereby permitting displacement of the active
element 6 by virtue of the energy stored therein.
[0042] The locking mechanism 2 can facilitate the locking of the
article 60 in the second position in several ways. For example, in
one embodiment, when split ring 10 is manufactured from an elastic
material of sufficient stiffness, it will expand and apply a radial
load against housing 3 after ring 14 cools below its transition
temperature. The elastic material may be a material that is not a
smart material, i.e., it does not require an external stimulus to
return to its original shape. Any subsequent attempt to further
extend connecting means 22 would then cause the spring stack 8 to
lock when loaded against the compression initiation element 4.
[0043] The article 60 in the FIG. 1 can be returned to its first
position manually if desired. In order to return the article 60 to
its first position, the manual force must be greater than the sum
of the spring constant of the expansion spring as well as the axial
frictional force between the compression initiation element 4 and
the inner surface of the housing 3.
[0044] The exemplary embodiment depicted in the FIG. 1 can be
varied to produce locking mechanisms that are capable of reversible
positioning of the article 60. In this embodiment, the active
element 6 comprises two springs, one capable of expanding and the
other capable of retracting. Upon activation of the expanding
spring, the article 60 moves away from the reference frame 50,
while upon activation of the retracting spring, the article 60
moves towards the reference frame 50. When the article 60 moves
towards the reference frame 50, the locking mechanism 2 permits it
to retain its position against compressive forces.
[0045] This exemplary embodiment facilitating the reversible
positioning of the article 60 is depicted in the FIG. 5. In this
embodiment, the active element 6 comprises a first spring 7 and a
second spring 9. Either the first spring 7 or the second spring 9
is manufactured from a smart material. When the first spring 7 is
manufactured from a smart material, the second spring 9 is
manufactured from a material that does not have memory retention
capabilities or vice-versa. In one embodiment, when the first
spring 7 is a retracting spring, the second spring 9 is an
expansion spring. In another embodiment, when the first spring 7 is
an expansion spring, the second spring 9 is a retracting
spring.
[0046] As depicted in the FIG. 5, the compression initiation
element 4 and the spring stack 8 are located between the first disc
24 and the second disc 25. The compression initiation element 4 is
constructed of the same materials and behaves in the same manner as
detailed above in the description of the FIG. 1. The spring stack 8
is located on the article (60) side of the compression initiation
element 4. The spring stack advantageously comprises wave springs
and behaves in a manner similar to that described above in the
description of the FIG. 1.
[0047] In the exemplary depiction of FIG. 5, the retraction spring
7 is manufactured from a material that does not display memory
retention properties. In other words, the retraction spring 7 is
not manufactured from a smart material. When the retraction spring
7 is activated it displaces the connecting means 22 towards the
reference frame 50. The expansion spring 9 is made from a smart
material such as, for example, a shape memory alloy. When the
expansion spring 9 is activated by the application of external
stimuli it has a spring constant k.sub.2 that is greater than the
spring constant k, of the retraction spring. Because of its greater
spring constant, the expansion spring can promote displacement of
the connecting means 22 towards the article 60.
[0048] In one embodiment, in one manner of operating the locking
mechanism 2 depicted in the FIG. 5, when it is desired to change
the position of the article 60 from a first position to a second
position an activating stimulus is supplied to the spring 9. The
activating stimulus is preferably a change in temperature brought
on by resistive heating. Upon heating the expansion spring 9 above
its transition temperature, the expansion spring promotes
displacement of the connecting means 22 towards the article 60. The
lightly loaded compression initiation element 4 and the unloaded
spring stack 8 will be pushed along by disk 24. Thus the
displacement of the expansion spring 9 promotes movement of the
article 60 towards its second position from the first position.
[0049] When the article 60 reaches the desired second position, the
activating stimulus is removed from the expansion spring 9. Any
loading of shaft 23 in the direction of element 50 will cause the
compression of the springs in the spring stack 8 between the
compression initiation element 4 and the disc 25. This compression
promotes the radial expansion of the springs in the spring stack 8.
The radial expansion of the springs in the spring stack 8 promotes
contact between the springs and the inner surface of housing 3 and
increases the axial friction between the springs and the housing 3.
The increase in the axial friction permits the locking of the
article 60 in the desired second position. Thus, the embodiment
depicted in the FIG. 5 can be advantageously used to resist
compressive loads.
[0050] In one embodiment, if the ring 14 is manufactured from a two
way shape memory alloy, the ring upon cooling returns to its
original shape and provides additional axial friction to assist
with the locking in the second position.
[0051] When the article 60 is to be returned to the first position,
the ring 14 is activated, thus unloading the spring stack 8. The
expansion spring 9 is not however activated during the desired
return. The compressive forces of the retraction spring 7 overcome
the extensional forces exerted by the expansion spring 9, thereby
returning article 60 to its first position.
[0052] In another embodiment, the locking mechanism 2 can be
returned to the first position manually after activation of ring
14. The retraction spring 7 reduces the manual forces that are
utilized to return the locking mechanism 2 to its first
position.
[0053] In yet another exemplary embodiment depicted in the FIG. 6,
the retraction spring 7 is manufactured from a smart material such
as, for example, a shape memory alloy, while the expansion spring 9
is manufactured from a material that does not have memory retention
capabilities. All the other components depicted in the FIG. 6
function in the same manner as those in the FIG. 5. The embodiment
depicted in the FIG. 6 can be advantageously used to resist tensile
loads.
[0054] In yet another embodiment depicted in the FIG. 7, the
locking mechanism 2 can resist both compressive and tensile loads.
In this embodiment, the locking mechanism comprises two compression
initiation elements 4 and 16 disposed on the shaft 22 of the
connecting means 23. The compression initiation elements are
disposed on opposing sides of the spring stack 8. In one exemplary
embodiment, the spring stack 8 comprises wave springs. The spring
stack 8 used in this embodiment comprises a dual wave spring stack.
As in the embodiments depicted in the FIGS. 5 and 6, the active
element 6 comprises a retraction spring 7 and an expansion spring
9. The expansion spring 9 comprises a shape memory alloy that can
be activated by the application of heat.
[0055] In one embodiment, in one exemplary method of operating the
locking mechanism depicted in the FIG. 7, the compression
initiation element 16 is first activated. Expansion spring 9
overcomes the force exerted by the non-activated retraction spring
7, thus promoting the extension of the locking mechanism 2 and the
displacement of the connecting means 22 towards article 60. After
element 14 of the compression initiation element 16 has been
deactivated, this mechanism will resist both compressive and
tensile forces. In another exemplary method of operating the
locking mechanism depicted in the FIG. 7, the compression
initiation element 4 is activated while the retraction spring 7 is
also activated thereby overcoming the spring constant of the
expansion spring 9. This facilitates the contraction of the locking
mechanism 2 and the connecting means 22 is displaced towards the
reference frame 50.
[0056] In one embodiment, by the application of a suitable external
stimulus, the locking mechanism 2 may promote a locking of the
article 60 in any desired position. The locking of the article is
accomplished at an load effective to prevent its being overcome by
the use of ordinary manual force, or the weight of the article, or
other forces of nature such as a wind, or the like. In one
embodiment, it is desirable to accomplish the locking in a manner
such that it cannot be overcome by the application of a force of
greater than or equal to about 10 kilograms. In another embodiment,
the locking is accomplished in a manner such that it cannot be
overcome by the application of a force of greater than or equal to
about 20 kilograms. In yet another embodiment, the locking is
accomplished in a manner such that it cannot be overcome by the
application of a force of greater than or equal to about 50
kilograms. In yet another embodiment, the locking is accomplished
in a manner such that it cannot be overcome by the application of a
force of greater than or equal to about 100 kilograms.
[0057] It is desirable to accomplish the positioning or
repositioning in a manner such that it can be accomplished by the
application of a force of less than or equal to about 10 kilograms.
In one embodiment, the positioning or repositioning is accomplished
by the application of a force of less than or equal to about 5
kilograms. In one embodiment, the positioning or repositioning is
accomplished by the application of a force of less than or equal to
about 2 kilograms.
[0058] It is desirable for the locking mechanism 2 to be capable of
imparting motion to an article 60 having a weight of about 0.5
kilogram (kg) to about 10,000 kilograms. In one embodiment, the
locking mechanism 2 can reposition an article a distance of about 1
micrometer to about 10,000 millimeters. In yet another embodiment,
the locking mechanism 2 has an accuracy of about 0.05 micrometers
to about 50 micrometers from a specified reference point and a
resolution of 0.25 millimeter. Further, the locking mechanism 2 is
capable of a full range of motion in a time period of about 1
second to about 10 minutes.
[0059] The locking mechanism 2 is advantageous in that it permits
positioning at any height or degree of opening depending upon the
physical characteristics of the person opening the article. The
detent capability exhibited by the wave spring locking mechanism
may be advantageously employed in automobile lift gates, tail
gates, doors, hoods, trunks, or the like. They may also be
advantageously employed in windows and doors for aircraft, ships,
residential and office buildings. The wave spring locking mechanism
may be advantageously employed in storm doors for residential and
office buildings.
[0060] While the disclosure has been described with reference to an
exemplary embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
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